4,256 research outputs found
Optimal control of many-body quantum dynamics: chaos and complexity
Achieving full control of the time-evolution of a many-body quantum system is
currently a major goal in physics. In this work we investigate the different
ways in which the controllability of a quantum system can be influenced by its
complexity, or even its chaotic properties. By using optimal control theory, we
are able to derive the control fields necessary to drive various physical
processes in a spin chain. Then, we study the spectral properties of such
fields and how they relate to different aspects of the system complexity. We
find that the spectral bandwidth of the fields is, quite generally, independent
of the system dimension. Conversely, the spectral complexity of such fields
does increase with the number of particles. Nevertheless, we find that the
regular o chaotic nature of the system does not affect signficantly its
controllability.Comment: 9 pages, 5 figure
Time-optimal control fields for quantum systems with multiple avoided crossings
We study time-optimal protocols for controlling quantum systems which show
several avoided level crossings in their energy spectrum. The structure of the
spectrum allows us to generate a robust guess which is time-optimal at each
crossing. We correct the field applying optimal control techniques in order to
find the minimal evolution or quantum speed limit (QSL) time. We investigate
its dependence as a function of the system parameters and show that it gets
proportionally smaller to the well-known two-level case as the dimension of the
system increases. Working at the QSL, we study the control fields derived from
the optimization procedure, and show that they present a very simple shape,
which can be described by a few parameters. Based on this result, we propose a
simple expression for the control field, and show that the full time-evolution
of the control problem can be analytically solved.Comment: 11 pages, 7 figure
Maximum population transfer in a periodically driven two-level system
We study the dynamics of a two-level quantum system under the influence of
sinusoidal driving in the intermediate frequency regime. Analyzing the Floquet
quasienergy spectrum, we find combinations of the field parameters for which
population transfer is optimal and takes place through a series of well defined
steps of fixed duration. We also show how the corresponding evolution operator
can be approximated at all times by a very simple analytical expression. We
propose this model as being specially suitable for treating periodic driving at
avoided crossings found in complex multi-level systems, and thus show a
relevant application of our results to designing a control protocol in a
realistic molecular modelComment: 7 pages, 6 figure
Finding a reflexive voice : -- researching the problems of implementing new learning practices within a New Zealand manufacturing organisation : a 100pt thesis presented in partial fulfilment of the requirements for the degree of Master of Management in Human Resources Management at Massey University
This study explored the social forces mediating manager's participation in a new reflexive participative learning practice designed to improve profitability within a New Zealand manufacturing organisation. Despite a large theoretical and managerial body of literature on organisational learning there has been little empirical investigation of how people experience and engage their reflexivity towards challenging the status-quo to create high level learning and new knowledge. Power was identified as a potential moderator of the reflexive learning experience and the variable relations of power and learning were constructed from a review of literature and these relationships were explored and investigated within the case study. Two prevailing discourses were identified as powerful moderators of public reflexivity, the traditionalist discourse which constructed managers actions and conversations towards insularism and survivalist concerns and the productionist discourse in which institutionalised production practices encircled and mediated managers actions and what constituted legitimacy in conversations. This study used a critical action research method to place the reflexive experience of managers and the researcher at the centre of the study and provide data representative of the social discourses that constructed variable freedoms and constraints upon the reflexive voice
Mapping Analysis in Ontology-based Data Access: Algorithms and Complexity (Extended Abstract)
Metamodeling and metaquerying in OWL 2 QL
OWL 2 QL is a standard profile of the OWL 2 ontology language, specifically tailored to Ontology-Based Data Management. Inspired by recent work on higher-order Description Logics, in this paper we present a new semantics for OWL 2 QL ontologies, called Metamodeling Semantics (MS), and show that, in contrast to the official Direct Semantics (DS) for OWL 2, it allows exploiting the metamodeling capabilities natively offered by the OWL 2 punning. We then extend unions of conjunctive queries with both metavariables, and the possibility of using TBox atoms, with the purpose of expressing meaningful metalevel queries. We first show that under MS both satisfiability checking and answering queries including only ABox atoms, have the same complexity as under DS. Second, we investigate the problem of answering general metaqueries, and single out a new source of complexity coming from the combined presence of a specific type of incompleteness in the ontology, and of TBox axioms among the query atoms. Then we focus on a specific class of ontologies, called TBox-complete, where there is no incompleteness in the TBox axioms, and show that general metaquery answering in this case has again the same complexity as under DS. Finally, we move to general ontologies and show that answering general metaqueries is coNP-complete with respect to ontology complexity, Î 2p-complete with respect to combined complexity, and remains AC0 with respect to ABox complexity
Editorial: ADAM10 in Cancer Immunology and Autoimmunity: More Than a Simple Biochemical Scissor
War and dissociation : the case of futurist aesthetics
Thanks to their deliberate engagement in state propaganda Italian Futurists deserved a prominent spot in the history of military aesthetics in the 20th century. However, under what looked like an unequivocal expression of support for war, lied a deep philosophical disagreement concerning its existential and epistemological value. The bone of contention concerned the effects of warfare on perception and, consequently, the means of its depiction. The author analyses this intellectual disagreement within the group and focuses, in particular, on its philosophical implications
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